After a wellbore has been drilled through a subterranean formation, the wellbore may be cased by inserting lengths of pipe (“casing sections”) connected end-to-end into the wellbore. Threaded exterior connectors known as casing collars may be used to connect adjacent ends of the casing sections at casing joints, providing a casing string including casing sections and connecting casing collars that extends from the surface towards the bottom of the wellbore. The casing string may then be cemented into place to secure the casing string within the wellbore.
Following the casing of the wellbore, the casing string may be perforated using a perforating gun to provide for fluid communication between the wellbore and the formation at desired locations, necessitating the ability to accurately position the perforating gun at the desired location within the wellbore. Therefore, a tool known as a casing collar locator (CCL) may be run into the wellbore along with the perforating gun on a wireline to confirm or correlate service depth using known reference points on the casing string. Particularly, as the CCL passes through a casing collar of the casing string, the magnetic lines of flux from the magnets are distorted, inducing a current in the coiled conductor known as a collar that is transmitted to the surface and recorded as a collar “kick”. The collar kick may be recorded in conjunction with a gamma ray or neutron porosity log to correlate the position of the casing collar (i.e., “cased hole log”) with the spontaneous potential (SP) or gamma ray signal of an open hole log. Following the correlation of the cased hole log with the open hole log, service depth may be determined by counting the casing collars of the casing string using the CCL as the CCL is displaced through the casing string.